The present invention relates to a combination formed of a rim provided with a circumferential bead-retaining protrusion and a tire with radial carcass reinforcement without an independent inner tube. It also concerns a special rim provided with at least one circumferential protrusion.
It is known that, under the combined effect of the multiple forces present between the contact surface of the tire and the ground, and with numerous torques affecting the wheel, substantial stresses are imposed on the beads of the tire, particularly in the event of a substantial loss of pressure and travel over a path of small radius. These stresses cause the axial displacement, towards the hollow part of the rim employed, of the bead which is furthest from the center of the path.
Various means are known which are directed at overcoming this problem, said means generally consisting of selecting a suitable shape for the rim profile. One of such means consists in retaining the bead by a circumferential protrusion which is arranged between the circumferential mounting groove and the frustoconical seat of the rim, said protrusion being generally referred to as a "hump". At present there are different forms of circumferential protrusions of standardized shape (for example, ETRTO standards). One can distinguish between:
the simple "hump" protrusion, having, in meridian section, a profile in the form of a circular arc;
the flat, so-called "flat hump", protrusion having, in meridian section, a profile which effectively comprises a flat portion.
Whether it be a "hump" or "flat hump", the diameter of the circumferential protrusion has a value which permits the bead of the tire to move past it upon the mounting on the rim. The compromise obtained with respect to the dislodging properties of the bead and the mounting-dismounting properties is not satisfactory.
There thus appeared a rim having asymmetrical protrusions ("asymmetric hump"): one protrusion has a height above the rim seat which varies circumferentially, passing from a maximum value to a minimum value along one diameter and from a minimum value to a maximum value along a second diameter, which is shifted axially with respect to the first diameter.
In the case of known tire beads, it does not seem that this rim solution has solved the problem, despite a greater height of protrusion than in the case of a circular protrusion or a flat protrusion.
In connection with the use of tires on rims with circumferential protrusion, it therefore appears necessary to modify the structure of the beads of these tires. French Patent 2 548 970 discloses such a modification; it concerns a bead of a tire intended to be mounted and used on a rim with flat protrusion. This bead is characterized by the combination of the meridian profile of its base, adapted to the profile of the seat of the mounting rim, and the axial location of its bead wire, said combination permitting a very substantial clamping of the bead on the rim without penalizing the mounting of the tire on the rim.
This solution is not ideal since the beads loosen from the rim seats under severe conditions of travel at pressures other than zero, these pressure values furthermore varying greatly as a function of the tolerances provided on the rims.